SDLP health spokesman Mark H. Durkan has urged people only to attend A&E at Altnagelvin if absolutely necessary following a Christmas spike in attendances.
The Foyle MLA said he understood Altnagelvin's casualty unit was almost at full capacity and asked members of the public to choose appropriate services if they are feeling unwell.
“Now that the Western Health Trust has introduced its 'Full Capacity Protocol' people should only attend the emergency department if it is absolutely necessary," he said.
"Clearly, the Trust has found itself in the situation where they are filled to capacity and where they have had to take extraordinary measures.
"I am assured they are doing all they can to ensure patients are seen as quickly as possible and emergency care must remain a priority.
“For some time the SDLP has warned of the deepening of our health crisis and the pressures staff are facing to deliver safe effect care.
"With growing waiting lists and fewer nurses, we cannot wait for action. Health must be prioritised and political leadership must step in. Transformation is no longer a goal, it is a necessity.
“There is nothing more precious that our health, we must act now before the crisis deepens and we run out of road," added the Foyle MLA.
In a joint statement the Health and Social Care Board (HSCB) and Public Health Agency (PHA) also asked people to show common sense when accessing health services that are in many cases already overburdened.
A spokesperson said: "Plans are in place across the Health and Social Care system to manage increased demand at this time. In the past week however some patients have had to wait longer to be treated in ED or to be admitted to hospital.
“We fully understand the distress and inconvenience this causes to patients and their families and staff are working hard to make sure patients’ needs are meet.
"A great many health and social care staff have shown tireless commitment and have gone the extra mile for patients and service users over the holiday period.
“We need the public’s continued help to ensure the sickest patients get the care they need and we urge people only use EDs for urgent and life threatening conditions.
"The most clinically urgent patients will continue to be prioritised and those with less serious needs should consider using alternative services to avoid lengthy waits.
“Another important/valuable way patients and their families can help is to work with Trust staff to facilitate timely hospital discharge arrangements.
"This may involve a temporary move to a nursing or residential home if a person cannot return home directly or while awaiting their preferred choice of accommodation.
"This would help people move from hospital to a more homely and appropriate environment which would meet their needs.
"Such a measure will also assist those awaiting admission to access hospital services promptly.”
GP Out of Hours Services have also been very busy over the holiday period.
The public are reminded that the GP Out of Hours service is for those with serious, urgent conditions that cannot wait until their own GP surgery reopens.
Staff will prioritise the most urgent and serious conditions. People with less urgent conditions may have to wait longer for a call back during busy periods.
They may wish to consider using alternative services such as seeking advice from their local pharmacist.
There are a range of alternative services that people can access if they do not need emergency care.
These include using the online A-Z symptom checker (https://www.nidirect.gov.uk/services/health-conditions-a-z) seeking advice from a pharmacist, going to a Minor Injury Unit, or contacting a GP or the GP Out of Hours services (if their medical condition can’t wait until the GP surgery reopens).
People can also check the average waiting times in their local Emergency Department.
For more information on ‘Staying Well’ this winter go to: https://www.nidirect.gov.uk/campaigns/stay-well.
For information on services over the New Year Holiday weekend see http://www.hscboard.hscni.net/health-care-services-christmas-new-year/.